Conventionally, an illuminating device that can output planar light has been known and used as a backlight unit for illuminating a liquid crystal display panel of a liquid crystal display device. As such an illuminating device for use in a liquid crystal display device, there exist illuminating devices of a direct type, a sidelight type, etc.
The direct type illuminating device has a configuration in which a light source is disposed immediately below a liquid crystal display panel. On the other hand, the sidelight type illuminating device has a configuration in which a light guide plate is disposed immediately below a liquid crystal display panel, and a light source is disposed in an opposed manner to a predetermined side end surface of the light guide plate (see, for example, Patent Document 1). In the sidelight type illuminating device, light emitted from the light source is introduced into the light guide plate via the predetermined side end surface of the light guide plate. The light thus introduced into the light guide plate is converted into planar light, and the liquid crystal display panel is illuminated with the planar light.
FIG. 4 is a simplified diagram of an example of a sidelight type illuminating device according to the conventional technique. With reference to FIG. 4, the conventional sidelight type illuminating device uses a plurality of light-emitting diode elements (LED) 101 as a light source. The plurality of LEDs 101 as the light source are mounted on a flexible printed circuit board 102 and arranged at a predetermined spacing from each other.
Furthermore, a light guide plate 103 that converts light from the LEDs 101 into planar light is made of a transparent plate-shaped member and has four side end surfaces as well as a front surface and a back surface that are perpendicular to the four side end surfaces. A predetermined one of the four side end surfaces of the light guide plate 103 is a surface to which the LEDs 101 are disposed in an opposed manner and functions as a light incidence surface for introducing light from the LEDs 101 into the light guide plate 103. Furthermore, the front surface of the light guide plate 103 is a surface that faces the side of a liquid crystal display panel (not shown) and functions as a light output surface for outputting in a planar shape, light introduced into the light guide plate 103 toward the side of the liquid crystal display panel.
According to the conventional technique, in order to allow effective incidence of light from the LEDs 101 on the light incidence surface of the light guide plate 103, the respective light-emitting surfaces of the LEDs 101 are located in close contact with the light incidence surface of the light guide plate 103. Furthermore, the LEDs 101 are fixed by a method in which part of the FPC 102 on which the LEDs 101 are mounted is bonded to the back surface of the light guide plate 103 using a double-sided adhesive tape (not shown).
Prior Art Document
Patent Document
    Patent Document 1: JP-A-2005-235560